Wire electric-discharge machining involves processing a workpiece such as metallic material, wherein an electrode wire is opposed to the workpiece with a suitable gap formed therebetween, causing electric discharge between the wire electrode and the workpiece through a medium such as water or the like displacing the wire electrode and the work relatively so as to cut or shape the work according to a predetermined pattern.
In electro-discharge machining as mentioned above, conventionally an elongated electrode wire with a 0.05 to 0.25 mm diameter is prepared and the electrode wire is fed to the work as the end portion of the wire is exhausted.
The following conditions are generally required of the wire electrode used in discharge machining,
(1) processing speed; a faster processing speed is required compared to the processing speed obtained by the conventional wire electrode;
(2) accuracy of the dimension and condition of the surface of the shaped workpiece; the shaping process must be done with high accuracy without causing pieces of the wire electrode to be sputtered onto the surface of the workpiece;
(3) workability; interruption of the wire electrode during the electric discharge machining must be decreased;
(4) cost; it is desired that the cost of the wire electrode must be as low as possible since the wire electrode is exhausted.
The processing speed may be made high by stabilizing the electric discharge between the wire electrode and the workpiece. However, the conventional wire electrode tends to cause the surface of the workpiece to be rough when the processing speed is fast.
In order to shape the work piece with high accuracy, it is necessary to use the wire electrode of a high accuracy diameter stretching the wire electrode with high tension. Therefore, the wire electrode must be strong enough to prevent break down of the wire by the tension.
In order to shape the surface of the workpiece and prevent formation of a rough surface, the electric discharge between the wire electrode and the workpiece must be stable and uniform. With the conventional wire electrode, it has been difficult to satisfy both requirements of increasing the processing speed and improving the accuracy of the workpiece with a good surface condition, therefore it is strongly desired to provide wire electrodes which satisfy the requirements as mentioned above.
In addition, the wire electrode may be broken down due to electrical shortage between the wire electrode and the workpiece, nonuniform discharge, or the tension loaded on the wire electrode; there are required a high accuracy of the wire, behavior of electric discharging and a high tensile strength.
Other requirements for the wire electrode are inexpensiveness of the alloy material and the workability of drawing wire into a thin wire such as 0.05 to 0.25 mm diameters.
Conventionally, as the wire electrodes, copper wires, brass wires (Cu containing 30% or 35% Zn) and tungsten wires have been used. However, the conventional wire electrodes made of the materials mentioned above do not fulfil the above mentioned requirements as explained hereinafter.
The copper wires tend to be broken down due to relatively low mechanical strength, and the processing speed is lower than that obtained with the use of the brass wires.
Although the brass wires can improve the processing speed compared to that of the copper wires, the processing speed obtained by the brass wires is still not sufficient. Futhermore, the brass wire electrodes can not provide a high size accuracy and a sufficient surface condition of the workpiece. The brass wire electrodes show another disadvantage in that the workability is not good.
The disadvantages of the tungsten wire electrodes are difficulty in wire drawing work and cost.
In order to eliminate the disadvantages as mentioned above, Japanese Patent Publication (Unexamined) Tokkai No. sho 59-50141 discloses the wire electrode material composed of essentially Cu including Zn of 20 through 50% by weight and one or more components of Ni, Co and Si with the total amount of 0.5 through 2% by weight. Futhermore, Japanese Patent Publication (Unexamined) Tokkai No. sho 57-41134 discloses the wire electrode material composed of essentially Cu including Zn of 5 through 40% by weight and Al of 0.1 through 4% by weight.
However, the former materials have the drawback that the workability of casting and wire drawing is inferior if Si is included more than 1.5% by weight. As to the latter material, sputtering of the wire electrode to the workpiece can not be suppressed in case of a high accuracy machining with pure water of high resistivity.